1. Technical Field
The present invention relates to a liquid ejecting apparatus, such as an ink jet printer, and a method of controlling a liquid ejecting apparatus and, more particularly, to a liquid ejecting apparatus provided with a liquid ejecting head that discharges a liquid droplet from a nozzle opening by means of a pressure generating unit being actuated through a supply of driving signal and a method of controlling the same.
2. Related Art
A liquid ejecting apparatus is provided with a liquid ejecting head that is capable of discharging liquid in the form of liquid droplets. The liquid ejecting apparatus is an apparatus that discharges various types of liquid from the liquid ejecting head. A typical example of the liquid ejecting apparatus may be, for example, an image recording apparatus, such as an ink jet printer (hereinafter, simply referred to as a printer), that discharges liquid ink in the form of ink droplets to be directed onto a recording sheet of paper, which serves as a discharge target object, to form dots for performing recording. In addition, in recent years, the liquid ejecting apparatus is not only used in the image recording apparatus but also used in various production equipments such as a display production equipment.
Here, taking the ink jet printer (hereinafter, simply referred to as a printer) for example, the printer has mounted a recording head that includes lines of ink flow passages that extend from a common ink chamber (reservoir) through pressure chambers to nozzle openings, pressure generating units (for example, piezoelectric vibrators) that change the volumes of the pressure chambers, and the like. The ink jet printer further includes a driving signal generating circuit (a driving vibration generating unit) that generates driving signals supplied to the pressure generating units. Then, the piezoelectric vibrators each are driven through a driving pulse included in a driving signal transmitted from the driving signal generating circuit to generate pressure fluctuation in the ink present in the pressure chambers and, using the pressure fluctuation, ink droplets are discharged from the nozzle openings. In accordance with the pressure fluctuation, pressure vibration of Helmholtz frequency in which the inside of each pressure chamber acts as an acoustic tube is excited over the ink present in each pressure chamber. The vibration period of this pressure fluctuation is expressed as a characteristic vibration period Tc.
However, after ink droplets are discharged, residual vibration in the ink present in the pressure chambers is problematic. That is, the behavior of meniscus is disturbed by the residual vibration and, thereby, ink droplets may be undesirably discharged or may adversely affect subsequent discharge action of ink droplets. Particularly, with the increase in recording speed and the increase in resolution of an recording image, when extremely fine (for example, a couple of pl) ink droplets are successively discharged at constant very short time intervals (for example, a couple of μs), it is desired that the residual vibration is suppressed as much as possible. For this reason, in this type of printer, a vibration damping element is included after a waveform element (discharge element) for discharging ink droplets within a driving signal, and the residual vibration is reduced by the vibration damping element, which is, for example, disclosed in JP-A-2002-127418(specifically, in FIG. 3).
Meanwhile, each of the piezoelectric vibrators, which serve as the pressure generating units, also has a vibration characteristic that is determined on the basis of its shape, material, or the like. The characteristic of vibration period of the piezoelectric vibrator may be, for example, denoted by Ta. The vibration of the characteristic vibration period Ta may be oscillated by performing expansion action with a time shorter than the characteristic vibration period Ta. The residual vibration of the piezoelectric vibrators may also adversely affect the discharge characteristics of ink droplets. Particularly, in a configuration in which a vibrator unit made by separating one piezoelectric material into a comb-shape is used and the separately cut piezoelectric vibrators correspond to the plurality of nozzle openings, an ink droplet is discharged from one of the nozzle openings and the residual vibration when discharging the ink droplet may be transmitted to another piezoelectric vibrator in the same vibrator unit. When the another piezoelectric vibrator is driven to discharge an ink droplet from the nozzle opening, there may be fluctuation in amount of ink droplets, fluctuation in flying speed or a decrease in discharge characteristics such as curve of flying.